Iraqi special forces have entered a town near Mosul hours after joining a massive operation to retake the Islamic State-held city.

An Associated Press reporter traveling with the elite force says they entered the town of Bartella from the east on Thursday after a heavy gunbattle that saw IS militants unleash a number of suicide truck bombs. It was not immediately clear if there had been any casualties.

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The long-awaited operation to retake Mosul began Monday and is expected to take weeks, if not months.

IS captured Iraq’s second largest city when it swept across the country in the summer of 2014. The group has suffered a string of defeats over the last year, and Mosul is its last urban bastion in Iraq.

Iraqi Prime Minister Haider al-Abadi said the battle to oust IS extremists from Mosul is going "more quickly than we thought."

Al-Abadi spoke in a video transmission Thursday to a diplomatic meeting about Mosul in Paris about stabilizing Iraq’s second-largest city. He didn’t provide details about the fighting.

Al-Abadi said that "our forces have started to move forward to free this city which was taken by IS over two years ago. The fighting forces are currently pushing forward toward the town more quickly than we thought, and more quickly certainly than we established in our plan of campaign."